1. Field of the Invention
The present invention relates to millimeter wave switches and more particularly to millimeter wave switches useful at millimeter wave frequencies and higher frequencies with increased power handling capability relative to known switches, amenable to being fabricated using microelectromechanical system (MEMS) technology.
2. Description of the Prior Art
RF switches are used in a wide variety of applications. For example, such RF switches are known to be used in variable RF phase shifters, RF signal switching arrays, switchable tuning elements, as well as band switching of voltage controlled oscillators. In order to reduce the size and weight of such RF switches, microelectromechanical system (MEMS) technology has been known to be used to fabricate such switches. An example of such an RF switch is disclosed in commonly owned U.S. Pat. No. 6,218,911, hereby incorporated by reference. The RF switch disclosed therein includes a pair of relatively parallel spaced apart metal traces. An air-bridged metal beam is disposed between the parallel spaced apart metal traces.
Electrostatic forces are used to deflect the air bridge to contact one of the metal traces. The center beam is attached to a substrate at each end. As such, when electrostatic attraction forces are applied, the beam deflects into a U-shaped configuration, such that a point approximately at the center of the beam, contacts one of the parallel metal traces disposed adjacent the beam. In such a configuration, the RF input is applied to one end of the beam.
Although such a configuration provides satisfactory performance, such a configuration has a relatively high impedance (i.e. relatively high inductive and resistance) which results in relatively high RF power losses, and reduces the RF power capability of the switch.
In order to solve the problem of high RF power losses of such switches, capacitive-type switches using MEMS technology have been developed for use in millimeter wave and microwave applications. Such capacitive-type switches include a lower electrode, a dielectric layer and a movable metal membrane. Electrostatic forces are used to cause the movable metal membrane to snap and make contact with the dielectric layer to form a capacitive-type switch. Examples of these capacitive-type switches are disclosed in: “Performance of Low Loss RF MEMS Capacitive Switches,” by Goldsmith et al., IEEE Microwave and Guided Wave Letters, Vol. 8, No. 8, August 1998, pgs. 269, 271; and “Ka-Band RF MEMS Phase Shifters,” by Pillans et al., IEEE Microwave and Guided Wave Letters, Vol. 9, No. 12, December 1999, pgs 520-522. Although such capacitive-type switches provide adequate performance in the millimeter wave and microwave frequencies, the dielectric layer in the capacitive-type switches is known to store charges making it unsuitable for commercial applications. Thus, there is a need for an RF switch which provides true metal-to-metal contact which avoids problems associated with capacitive-type switching and also provides increased RF power handling capability relative to known RF switches.